Polish President Bronislaw Komorowski cancelled a planned meeting on Monday with Ukrainian counterpart Viktor Yanukovych to instead hold top-level talks on the situation across the border.
Poland, a strong advocate of Ukraine's entry into the European Union, "will make sure that the door to Europe will always remain open to Ukraine", Komorowski told reporters after the Warsaw talks.
Several other countries in the region also expressed their concern Monday over the mounting unrest in Ukraine, as thousands of Ukrainian demonstrators blockaded government buildings in Kiev in the hopes of forcing out those in power.
But special EU envoy Aleksander Kwasniewski said Yanukovych was unlikely to heed the opposition's call to resign.
"It is much more likely that tougher measures like the introduction of an emergency situation in Kiev or over a larger part of the country will be used," the former Polish president told Poland's RMF radio.
Rumours have been circulating that Ukraine will declare a state of emergency in Kiev, where demonstrators declared a general strike on Monday.
Ukrainian Foreign Minister Leonid Kozhara however assured Polish counterpart Radoslaw Sikorski in a telephone call that his government had no plans to do so.
The Lithuanian foreign ministry meanwhile summoned the Ukrainian ambassador to Vilnius on Monday to express "its concerns about the violent dispersal of peaceful demonstrators on Independence Square" in Kiev on Saturday.
It also "stressed the need to investigate and duly punish the culprits", according to a ministry statement.
'The marks of an imperialist policy'
Kiev surprised Europe last week by ceding to Russian pressure at the 11th hour and refusing to sign a landmark pact with the EU that would have seen it break away from former master Russia.
Ukraine's decision to scrap the Association Agreement, which had been months in the making, has unleashed a war of words between East and West recalling Cold War days and sparked some of the biggest protests seen in Ukraine in a decade.
"Russia has divulged the goal of its foreign policy towards members of the Commonwealth of Independent States (CIS), which is to not let them move closer to the European Union," Wojciech Konanczak, an analyst at Poland's Centre for Eastern Studies, told AFP.
Kiev's decision "is a success for Russia", he said, adding that the crisis in EU-Ukraine relations would only deepen the longer the current situation persists.
What is more, he said, "Moscow has made it clear that it will not limit its actions to Ukraine, but will also target Moldova, as it did with Armenia", which wound up joining a Moscow-led Customs Union.
Komorowski adviser Roman Kuzniar said the EU must play a decisive role in stopping Moscow from pushing through its plans in the region.
"The EU has enough potential to neutralise Moscow's actions, which threaten the sovereignty of a country and which bear the marks of an imperialist policy," he told AFP.
Lithuanian President Dalia Grybauskaite, whose ex-Soviet country currently holds the rotating EU presidency, for her part urged Ukraine to make "strategic decisions".
"Ukraine's authorities and opposition must come to an agreement through peaceful and democratic means," she said in a statement sent to AFP.
Calls for a peaceful solution also came from other European politicians, including Swedish Foreign Minister Carl Bildt -- another strong proponent of Ukraine's integration into the EU -- and his Czech and Slovak counterparts, as well as officials in Brussels.
"The demonstrations send a very clear message," said Steffen Seibert, spokesman for German Chancellor Angela Merkel.